1. Field of the Invention
The present invention provides a voltage clamper, and more particularly, to a voltage clamper capable of providing a corresponding voltage drop according to an external input voltage.
2. Description of the Prior Art
With the progressive development of semiconductor processes, many different circuits are integrated into integrated circuits to drive the development of electronic products. For example, one memory chip may comprise a plurality of memory cells for storing data. Owing to the development of semiconductor processes, more memory cells are accommodated in a same area on a memory chip. Typically, the operation voltages of internal devices are limited in a voltage range according to the spec of integrated circuits. For example, the operation voltage of the above-mentioned memory chip must be limited in a voltage range to allow the memory chip to function normally. When the operation voltage supplied to the memory chip is too high, structural damage to the memory cells in the memory chip may cause reliability issues in data storage of memory cells. Oppositely, the operation voltage may not be able to successfully drive the memory cells to store data in a predetermined period of time when the operation voltage supplied to the memory chip is too low. Therefore, the memory chip must operate under a low clock. In other words, an operation voltage that is too low will affect the performance of the memory chip greatly.
Generally speaking, the same memory chip can be applied to different devices and used for storing data temporarily. However, different devices may be supplied with different external voltages. For example, the power supply module of one device provides a voltage level of 3.6V, but the power supply module of another device provides a voltage level of 1.6V. Therefore, the prior art memory chip utilizes a voltage drop circuit to transform the external voltage to the internal operation voltage that is applicable to the memory chip. For example, the voltage drop circuit may generate a fixed voltage drop of 1V. Under the circumstances, the range of the operation voltage of the memory chip to function normally is 2.6V-1.6V, based on the spec of the voltage drop circuit. In other words, the memory chip having such a voltage drop circuit can be only applied to devices supplied with an external voltage ranging from 3.6V to 2.6V. When the memory chip having such a voltage drop circuit is applied to a device supplied with an external voltage of 4V, the operation voltage of the memory chip will exceed the normally functional range of the operation voltage of the memory chip (2.6V-1.6V), since the operation voltage of the memory chip, used for driving the internal memory cells, is 3V after the voltage drop circuit applies a voltage drop of 1V to the external voltage. As a result, reliability issues arise when the memory chip is storing data. Similarly, the operation voltage of the memory chip, used for driving the internal memory cells, is 1V after the voltage drop circuit applies a voltage drop of 1V to the external voltage when the memory chip having such a voltage drop circuit is applied to a device supplied with an external voltage of 2V. Since 1V is not within the normally functional range of the operation voltage of the memory chip (2.6V-1.6V), the performance of the memory chip is greatly affected due to this operation voltage that is too low, as mentioned previously.
Since a fixed voltage drop is generated by the voltage drop circuit utilized in the prior art memory chip, the application range of the memory chip is limited by the fixed voltage drop. As mentioned previously, the memory chip can be only applied to devices supplied with an external voltage ranging from 3.6V to 2.6V because a 1V voltage drop is generated by the voltage drop circuit and the normally functional range of the operation voltage of the memory chip is 2.6V-1.6V. When the memory chip is applied to a device supplied with an external voltage of 4V, the voltage drop circuit on the memory chip needs to be re-designed to lift the voltage drop generated by itself. Similarly, when the memory chip is applied to a device supplied with an external voltage of 2V, the voltage drop circuit on the memory chip also needs to be re-designed to reduce the voltage drop generated by itself. Therefore, the production cost of the memory chip is greatly raised to make the memory chip not competitive.